1. Field of the Invention
The present invention generally relates to a white balancing adjusting apparatus. More specifically, the present invention is directed to a white balance control used in a camera and the like.
2. Description of the Prior Art
In most of recently available video cameras, the data about the brightness (Y1) signal and the color difference (R-Y and B-Y) signals required to control the white balance are detected from a frame of picture. In this case, these conventional video cameras are arranged in order that signal detecting precision is increased by subdividing a frame of picture into a plurality of windows, and by integrating such brightness and color difference signal data with respect to each of the plurality of windows. That is, the white balance control is correctly performed in such a manner that a window grid having a preselected dimension is preset to subdivide a frame of picture, and data about brightness and color difference information derived from the respective windows are integrated so as to detect improper portions which are not suitable to the white balance control, for instance,a window whose brightness is too high and/or too low to detect correct color component, and thereafter the data derived from these improper windows are eliminated from the entire data for the correct white balance control.
Referring now to FIG. 1, an example of an arrangement of the above-described conventional white balance control system will be explained. In the white balance control system of FIG. 1, reference numeral 3, shows an integration adder, reference numeral 4 denotes an integration register (simply, referred to "Reg"), and reference numeral 5 represents a window generating circuit (simply, referred to "Win Gen") for generating a signal by which a frame of picture is subdivided into plural windows and positions of these windows are designated. Further, reference numeral 6 denotes an image pickup device (CCD), reference numeral 7 shows a digital signal processing circuit (DSP) having A/D converters in input/output stages; and reference numeral 8 is a white balance control circuit (WB Cont). It should be understood that although only a single circuit arrangement of the integration circuits 3 and 4 is shown for the sake of simple illustration, three circuit arrangements for the brightness(Y1) signal and the color difference (R-Y and B-Y) signals are actually employed. An image of an object is passed through an image pickup optical system (not shown in detail) and then focused onto the image pickup device 6. An analog image signal obtained from the image pickup device 6 is processed by the analog-to-digital (A/D) converter, and thereafter is processed in the digital signal processing circuit 7. Then, the digital processed image signal is D/A-converted to be outputted as a video signal. On the other hand, the brightness (Y1) signal and the two color difference (R-Y and B-Y) signals are derived as white balance controlling data during the data process from the digital signal processing circuit 7. These three signals are inputted into the integration circuit constructed of the adder 3 and the register 4, so that these white data are integrated. When this integration process is carried out, the window signal "W" which has been generated from the window generating circuit 5 and which subdivides the picture into a plurality of windows will determine which window's data are integrated. The integration circuits 3 and 4 sequentially acquire the data of a portion of the picture in response to the window signal "W", and then the acquired data are transferred to the white balance control circuit 8. Upon completion of the data acquisition performed in this manner with respect to one picture, the white balance control circuit 8 eliminates the color difference data about the subdivided picture portion which is not suitable for the white balance control (for instance, window portion "S" as shown in FIG. 2(b)) due to excessive brightness thereof among the acquired data based on the integrated data of the brightness data. Then, the white balance control circuit 8 uses only the effective data, which have not been eliminated, in order that the white balance control in the digital signal processing circuit 7 is carried out.
However, the above-described prior art has following drawbacks. That is, when the picture portions (windows) not suitable for the white balance control, such as too high brightness picture portions, are removed from the entire picture, if the size of the window is excessively large, then a large area of such improper picture portions will be eliminated. As a result, the correct detection of the white balance controlling data cannot be carried out. Conversely, when the size of the window is excessively small, a lengthy time period is required to acquire the correct white balance controlling data. For instance, as illustrated in FIG. 2(c), when the window size is too large, even if a small-sized higher brightness portion such as "T" is present, all of the color information data signals within the window containing this high brightness portion will be eliminated from the data acquisition for white balance control. To the contrary, as shown in FIG. 2(d), when the window size is too small, precision in the white balance control is not seriously deteriorated even if the improper picture portion (window) indicated by a symbol "U" is eliminated from the data acquisition for the white balance control. However, there is another problem that since a total number of such windows is considerably greater than that of FIG. 2(c), a lengthy data acquisition for one frame of picture is required.
The present invention has been made in an attempt to solve the above-described conventional problems, and therefore, has an object to provide a white balance adjusting apparatus capable of acquiring correct data for a white balance control by properly eliminating information about a picture portion from which color components cannot be correctly detected such as an excessively high brightness picture portion and/or an excessively low brightness picture portion, while a total number of windows for subdividing one picture into plural picture portions is unchanged.